Method and apparatus for short handover latency in wireless communication system using beam forming

ABSTRACT

Beam selection is provided. A method for handover in a mobile station includes sending a scan request message for scanning a downlink (DL) beam with respect to a serving base station (BS) and a neighboring BS, to the serving BS, and receiving a scan response message; determining the DL beam for the MS by performing scanning with the serving BS and the neighboring BS based on the scan response message; sending a scan report message comprising a result of the scanning to the serving BS; when receiving an air-HO request message from the serving BS, generating an air-HO response message comprising information of a neighboring BS to which the MS hands over based on the air-HO request message; performing beam selection with the neighboring BS of the handover based on the air-HO request message; and performing the handover.

CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY

The present application claims the benefit under 35 U.S.C. §119(a) to aKorean patent application filed in the Korean Intellectual PropertyOffice on Sep. 29, 2011, and assigned Serial No. 10-2011-0098916, theentire disclosure of which is hereby incorporated by reference.

TECHNICAL FIELD OF THE INVENTION

The present disclosure relates generally to a beamforming system. Moreparticularly, the present disclosure relates to a method and anapparatus for improving handover latency matter due to beamforming usedto support a wider coverage in a wireless communication system.

BACKGROUND OF THE INVENTION

The advent of smart phones exponentially increases user traffic, thatis, data usage. Hence, users demand high data throughput more and more.This implies that a high bandwidth is required. For doing so, a highfrequency needs to be used.

However, the higher frequency raises signal attenuation per distance.That is, when a center frequency over 30 GHz is used, base stationcoverage reduction caused by the signal attenuation is inevitable. Thecoverage reduction requires more beam use, which increases latency.Thus, a method and an apparatus for enhancing the latency are needed.

SUMMARY OF THE INVENTION

To address the above-discussed deficiencies of the prior art, it is aprimary aspect of the present disclosure to provide a method and anapparatus for short handover latency in a wireless communication systemusing beamforming.

Another aspect of the present disclosure is to provide a method and anapparatus for conducting beam selection in a scanning interval inadvance in a wireless communication system using beamforming.

Yet another aspect of the present disclosure is to provide a method andan apparatus for minimizing handover latency increase in beam selectionby omitting the beam selection in handover using downlink/uplink linkbeam information prestored.

According to one aspect of the present disclosure, a method for handoverin a Mobile Station (MS) of a wireless communication system whichadjusts a beam direction includes sending a Scan_Request message forscanning the best DownLink (DL) beam or the best DL beam and UpLink (UL)beam with respect to a serving Base Station (BS) and a neighboring BS,to the serving BS, and receiving a Scan_Response message; determiningthe best DL beam or the best DL beam and UL beam for the MS byperforming Scanning or the Scanning and Association with the serving BSand the neighboring BS based on the Scan_Response message; sending aScan_Report message comprising a result of the Scanning or the Scanningand the Association to the serving BS; when receiving an Air-HO_Requestmessage from the serving BS, generating an Air-HO_Response messagecomprising information of a neighboring BS to which the MS hands over,based on the Air-HO_Request message; performing beam selection with theneighboring BS of the handover based on the Air-HO_Request message; andperforming handover, and transmitting and receiving data to and from theneighboring BS of the handover.

According to another aspect of the present disclosure, a method forhandover in a serving BS of a wireless communication system whichadjusts a beam direction includes receiving a Scan_Request message forscanning the best DL beam or the best DL beam and UL beam for an MS,from the MS, receiving a Dedicated Ranging Code of the MS from aneighboring BS through negotiation with the neighboring BS, and sendinga Scan_Response message comprising information about whether to performScanning or the Scanning and Association, to the MS; receiving from theMS a Scan_Report message comprising information of the best DL beam orthe best DL beam and UL beam for the MS and a result of the Scanning orthe Scanning and the Association; sending a NW-HO_Request message to atleast one neighboring BS based on the Scan_Response message in order toidentify a BS capable of supporting handover of the MS and to sharecontext of the MS; receiving a NW-HO_Response message comprisinginformation indicating whether the handover of the MS is supportable,from the at least one neighboring BS; sending an Air-HO_Request messageto the MS based on the NW-HO_Response message, and receiving anAir-HO_Response message comprising information indicating whether the MSis able to hand over and information of at least one neighboring BS towhich the MS hands over; and sending a NW-HO_Confirm message informingwhether the handover of the MS is performed, to the neighboring BS whichsends the NW-HO_Request message based on the Air-HO_Response message.

According to yet another aspect of the present disclosure, a method forhandover in a neighboring BS of a wireless communication system whichadjusts a beam direction includes sending a Dedicated Ranging Code of anMS to a serving BS through negotiation with the serving BS, andperforming Association with the MS to scan the best DL beam or the bestDL beam and UL beam for the MS; receiving from the serving BS aNW-HO_Request message based on a Scan_Response message comprising aresult of Scanning or the Scanning and Association of the MS in order toidentify a BS capable of supporting handover of the MS and to sharecontext of the MS; generating and sending a NW-HO_Response messagecomprising information indicating whether the handover of the MS issupportable, to the serving BS; receiving from the serving BS aNW-HO_Confirm message informing whether the handover of the MS isperformed, to the neighboring BS which sends the NW-HO_Request messagebased on the Air-HO_Response message; performing beam selection with theMS based on the NW-HO_Confirm message; and transmitting and receivingdata to and from the MS which hands over.

According to still another aspect of the present disclosure, anapparatus of an MS for handover in a wireless communication system whichadjusts a beam direction includes a receiver for receiving at least onereference signal from a BS in at least one DL Tx beam direction; atransmitter for sending a ranging signal to the BS in at least one UL Txbeam direction; a channel estimator for estimating a channel accordingto the at least one DL Tx beam direction using the at least onereference signal; and a controller for selecting best DL and UL beamsbetween the BS and the MS by considering channel information accordingto the at least one DL Tx beam direction, and controlling to send andreceive messages to and from the BS.

According to a further aspect of the present disclosure, an apparatus ofa serving BS for handover in a wireless communication system whichadjusts a beam direction includes at least one antenna comprising aplurality of antenna elements; a transmitter for sending at least onereference signal in at least one DL Tx beam direction; a receiver forreceiving channel information according to at least one UL Tx beamdirection from an MS; a controller for selecting the UL Tx beamdirection by considering the channel information according to at leastone UL Tx beam direction received from the MS through the receiver,selecting best DL beam and UL beam between the MS and the serving BS bysending and receiving messages for the MS in consideration of theselected UL Tx beam direction, and providing information for handover tothe MS; and a plurality of Radio Frequency (RF) paths connected to therespective antenna elements, and forming a beam to send a signal to theMS according to the DL Tx beam direction selected by the controller.

According to a further aspect of the present disclosure, an apparatus ofa neighboring BS for handover in a wireless communication system whichadjusts a beam direction includes at least one antenna comprising aplurality of antenna elements; a transmitter for sending at least onereference signal in at least one DL Tx beam direction; a receiver forreceiving channel information according to at least one UL Tx beamdirection from an MS; a controller for selecting the UL Tx beamdirection by considering the channel information according to at leastone UL Tx beam direction received from the MS through the receiver,selecting best DL beam and UL beam between the MS and the serving BS bysending and receiving messages for the MS in consideration of theselected UL Tx beam direction, and providing information for handover tothe serving BS; and a plurality of RF paths connected to the respectiveantenna elements, and forming a beam to send a signal to the MSaccording to the DL Tx beam direction selected by the controller.

Other aspects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, itmay be advantageous to set forth definitions of certain words andphrases used throughout this patent document: the terms “include” and“comprise,” as well as derivatives thereof, mean inclusion withoutlimitation; the term “or,” is inclusive, meaning and/or; the phrases“associated with” and “associated therewith,” as well as derivativesthereof, may mean to include, be included within, interconnect with,contain, be contained within, connect to or with, couple to or with, becommunicable with, cooperate with, interleave, juxtapose, be proximateto, be bound to or with, have, have a property of, or the like; and theterm “controller” means any device, system or part thereof that controlsat least one operation, such a device may be implemented in hardware,firmware or software, or some combination of at least two of the same.It should be noted that the functionality associated with any particularcontroller may be centralized or distributed, whether locally orremotely. Definitions for certain words and phrases are providedthroughout this patent document, those of ordinary skill in the artshould understand that in many, if not most instances, such definitionsapply to prior, as well as future uses of such defined words andphrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

FIG. 1 illustrates downlink beam transmission and reception according toan exemplary embodiment of the present disclosure;

FIG. 2 illustrates coarse beam and fine beam selection according to anexemplary embodiment of the present disclosure;

FIG. 3 illustrates uplink beam transmission and reception according toan exemplary embodiment of the present disclosure;

FIG. 4 illustrates a handover delay time according to an exemplaryembodiment of the present disclosure;

FIG. 5 illustrates message flows of the handover according to anexemplary embodiment of the present disclosure;

FIG. 6 illustrates operations of a mobile station according to anexemplary embodiment of the present disclosure;

FIG. 7 illustrates operations of a serving base station according to anexemplary embodiment of the present disclosure;

FIG. 8 illustrates operations of a neighboring base station according toan exemplary embodiment of the present disclosure;

FIG. 9 illustrates a transmitting stage according to an exemplaryembodiment of the present disclosure; and

FIG. 10 illustrates a receiving stage according to an exemplaryembodiment of the present disclosure.

Throughout the drawings, like reference numerals will be understood torefer to like parts, components and structures.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 through 10, discussed below, and the various embodiments used todescribe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged system or device. The followingdescription with reference to the accompanying drawings is provided toassist in a comprehensive understanding of exemplary embodiments of theinvention as defined by the claims and their equivalents. It includesvarious specific details to assist in that understanding but these areto be regarded as merely exemplary. Accordingly, those of ordinary skillin the art will recognize that various changes and modifications of theembodiments described herein can be made without departing from thescope and spirit of the invention. In addition, descriptions ofwell-known functions and constructions may be omitted for clarity andconciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of theinvention. Accordingly, it should be apparent to those skilled in theart that the following description of exemplary embodiments of thepresent invention is provided for illustration purpose only and not forthe purpose of limiting the invention as defined by the appended claimsand their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

By the term “substantially” it is meant that the recited characteristic,parameter, or value need not be achieved exactly, but that deviations orvariations, including for example, tolerances, measurement error,measurement accuracy limitations and other factors known to those ofskill in the art, may occur in amounts that do not preclude the effectthe characteristic was intended to provide.

The present disclosure relates to a method and an apparatus forenhancing handover latency increase which can result from beamformingused to support a wider coverage in a millimeter wave wirelesscommunication system using a high frequency over 30 GHz.

Exemplary embodiments of the present disclosure provide a method and anapparatus for short handover latency in a wireless communication systemusing beamforming.

FIG. 1 depicts DownLink (DL) beam transmission and reception accordingto an exemplary embodiment of the present disclosure.

Referring to FIG. 1, in the DL, a Base Station (BS) 110 transmits data(including a broadcast message) by changing a DL Tx beam direction usingan array antenna. Next, a Mobile Station (MS) 120 receives the data bychanging an Rx beam direction.

To attain maximum data throughput between the BS 110 and the MS 120, theDL Tx beam of the BS 110 should face the MS 120 and an active arrayantenna for the DL Rx beam of the MS 120 should also face the BS 110.

FIG. 2 depicts coarse beam and fine beam selection according to anexemplary embodiment of the present disclosure.

Referring to FIG. 2, an MS 220 sets a direction for the DL Rx beam andthen attempts to receive DL Tx beams of a BS 210. Herein, the MS 220 canreceive a preamble over a Synch CHannel (SCH). The preamble includes abeam ID. Alternatively, the beam ID can be contained in a BroadcastCHannel (BCH) following the SCH, and a message in the BCH is carried byover the DL Tx beam such as the SCH, as in the transmission over theSCH. Frame structure may be different based on design philosophy.

The MS 220 repeats this process by changing the DL Rx beam. Next, the MS220 determines which DL Tx beam of the BS 210 has the greatest signalstrength.

Next, the MS 220 notifies a beam ID of the DL Tx beam of the greatestsignal strength to the BS 210, in a ranging procedure to be explained.

As such, the MS 220 and the BS 210 determine the DL Tx/Rx beams to useand finish DL data transmission/reception preparation. This can bereferred to as a beamforming basic procedure, and coarse beam selection.

For coverage expansion and reliable data transmission in view ofoptimization, additional beamforming can be carried out. That is, anarrower beam than the beam width used in the coarse beam selection canbe selected, which is referred to as fine beam selection.

Unlike the wide beam used in the SCH/BCH, a reference signal (e.g., apreamble), a midamble, or a corresponding signal from the BS 210 isused, and the reference signal includes a fine (or narrow) beam ID.

The reference signal is transmitted from the BS 210 to the MS 220 overthe DL fine (or narrow) Tx beams. The MS 220 receives the signal bychanging the direction of the DL Rx beams with respect to the DL fine(or narrow) Tx beams of the BS 210, measures a channel, and thendetermines the direction of the DL fine (or narrow) Rx beam. Thisprocess is repeated as many times as the DL fine (or narrow) Rx beams ofthe MS 220. In other words, the selection of the BS fine (or narrow)beam and the MS wide or fine (or narrow) beam in the DL can be the finebeam selection.

Through the fine beam selection, the MS 220 can identify the DL fine (ornarrow) Rx beam of the coarse beam selection and the DL fine (or narrow)Tx beam of the greatest signal strength.

Next, the MS 220 informs the BS 210 of the DL fine (or narrow) Tx beam(the DL fine (or narrow) Tx beam to be used by the BS 210 to transmitdata to the MS 220).

FIG. 3 depicts UpLink (UL) beam transmission and reception according toan exemplary embodiment of the present disclosure.

Referring to FIG. 3, the UL also requires the beam selection as in theDL. Such beam selection is similar to the DL coarse beam selection butthe beam is selected in a ranging procedure of an MS 320, rather thanthe SCH/BCH.

That is, the MS 320 sends a ranging code over the UL Tx beam, and theranging code includes the DL Tx beam ID (the DL Tx beam of the BS havingthe greatest signal strength identified/selected through the MS coarsebeam selection in the DL) as in the coarse beam selection. This impliesthe signal strength of the best TX beam of the BS represents the signalstrength of the BS. In case of omni-directional antenna system, only onesignal strength from the BS is measured. But. For Beam Forming System,multiple beams from one BS exist and the MS will measure the signalstrength of each beam. Eventually, one best beam of BS represents thesignal of the BS like the case of BS having omni-directional antenna(i.e. a sort of single beam). The ranging code also includes the UL Txbeam ID so that the BS can identify the UL Tx beam including the rangingcode received from the MS. The MS 320 sends the ranging code by changingthe UL Tx beam. This process is repeated multiple times as many as theUL Rx beams of the BS 310. FIG. 3 depicts the single UL Rx beam by wayof example. When the BS includes a plurality of UL Rx beams, the BS 310can repeatedly receive the UL Rx beam of the MS by changing the UL Rxbeams and then determine which UL Tx beam of the MS 320 has the greatestsignal strength.

To notify the UL Tx beam to be used by the MS 320 to transmit data, theBS 310 sends a message such as RNG-ACK to the MS 320.

Hence, the MS 320 finishes the UL data transmission and receptionpreparation with the BS 310. Notably, the fine beam selection can beperformed as in the DL. However, since the fine (or narrow) beamgeneration in the compact MS generally consumes great power andincreases implementation complexity, the wide beam is mostly used.

Since the MS 320 is mostly mobile, the direction change of the DL Txbeam/UL Rx beam of the BS 310 and the DL Rx beam/UL Tx beam of the MS320 is inevitable. For doing so, the MS 320 and the BS 310 need toperiodically change the beam in order to find the best beam for eachother, which is referred to as beam tracking.

Through the beamforming as stated above, the coverage improvement(expansion) and the more reliable data transmission are possible.However, to initiate the data communication after physicalsynchronization with one BS, the MS and the BS require the beamselection, which can increase latency. While the latency in the beamselection is not a considerable problem in initial network entry, thelong handover latency caused by the beam selection during the handovercan be burdensome.

FIG. 4 depicts a handover delay time according to an exemplaryembodiment of the present disclosure.

Referring to FIG. 4, an MS 420 performs the beam selection for the DLreception. A BS 410 sends its preamble over the SCH. To receive thepreamble, the MS 420 seeks the beam receiving the preamble of thegreatest signal power level by changing the Rx beam. In FIG. 4, WBdenotes the wide beam.

This process requires an additional time as long as M×N (M: the totaltime required to receive all of the DL Tx beams of the BS 410 over oneDL Rx beam of the MS, N: the number of the DL Rx beams), and directlyaffects the handover latency.

When the MS 420 performs the ranging, the MS 420 sends the ranging codeby changing the UL Tx beam. Such UL Tx beam transmission is repeated asmany times as the number of the UL Rx beams of the BS 410. That is, anadditional time as long as M′×N′ (M′: the time required for the MS toreceive all of the UL Tx beams of the MS over one UL Rx beam, N′: thenumber of the UL Rx beams of the BS) is required. Such a time candirectly affect the handover latency.

FIG. 5 illustrates a message flow diagram of the handover according toan exemplary embodiment of the present disclosure.

Referring to FIG. 5, for the handover of an MS 510, a serving BS 520 andneighboring BSs 530 and 540 should measure the channel. The channelmeasurement is referred to as scanning. For the scanning, the MS 510 andthe serving BS 520 need control message transaction.

For example, the scanning is fulfilled throughScan_Request/Scan_Response message transaction (steps 1-1 and 1-2). Howto conduct Scanning/Association, to be explained, is determined in theScan_Request/Scan_Response message transaction.

Parameters of the Scan_Request/Scan_Response messages are as follows.

Scanning Type indicates a scanning type and classified into two types ofScanning only (0), and Scanning and Association (1). The Scanning only(0) indicates only the scanning performed, and the Scanning andAssociation (1) indicates both of the Scanning and the Associationperformed (step 1-3).

Scanning iteration indicates how many times the scanning is repeated;that is, how many times (scanning duration+interleaving interval) isiterated.

Scanning duration indicates a duration when the MS 510 scans (selectsthe coarse beam and measures the channel) the serving BS 520 and theneighboring BSs 530 and 540. When the BS (e.g., the serving BS 520)determines that the communication with the MS is infeasible in thisduration, and thus does not transmit the data to the MS 510.

Scanning interleaving interval is an interval between the Scanningduration and the Scanning duration, where the BS (e.g., the serving BS520) and the MS 510 can communicate. In this interval, the MS 510reports the scanning result to the BS (e.g., the serving BS 520).

Scanning metric indicates a measurement metric, and is used to setReceived Signal Strength Indication (RSSI), Carrier toInterference-and-Noise Ratio (CINR), and RTD.

Scanning Report Type is used to determine a method for reporting themeasurement result to the BS. Periodic Reporting or Event-drivenReporting can be set. the Periodic Reporting indicates periodic report,and the Event-driven Reporting indicates report when an event occurs.

Report Period is an additional period required when the ScanningReporting Type indicates the Periodic Reporting, that is, indicates theperiod for the MS 510 to transmit the channel measurement result to theBS 520. Herein, various units can be used. For example, the time or aframe number can be used. Herein, the number of Scanning ListeningIntervals can be used. That is, when the value is 5, the MS 510 needs toreport the measurement result of at least one Scanning Duration to theMS 520 in every fifth Scanning Listening Interval.

Report Condition is a parameter included when the Scanning ReportingType is the Event-driven Reporting. The MS 510 obtains the ReportCondition using information (Report Condition) relating to theEvent-driven Reporting broadcast by the serving BS 520 or using ReportCondition information of the Scan_Response. When the channel measurementresult satisfies the Report Condition (e.g., a CINR difference betweenthe neighboring BSs 530 and 540 and the serving BS 520 is greater than 3dB), the MS 510 can send the Scanning Report to the BS 520 during arandom Scanning Interleaving Interval. In some implementations, theScanning Report can be transmitted in the Scanning Duration.

BSID is used to designate the BS to scan.

Dedicated Ranging Code indicates a Dedicated Ranging Code to be used bythe MS 510 in the corresponding BS having a particular BSID in theprocess of the Association.

Dedicated Ranging Opportunity is used to indicate Dedicated RangingOpportunity of the MS 510 for the MS 510 to transmit the DedicatedRanging Code, and includes location information and size information.

Period for Dedicated Ranging Code indicates a valid time of theDedicated Ranging Code of the MS 510 transmitted in the corresponding BSin the process of the Association, and functions as a timer. That is,when the Period for Dedicated Ranging Code expires, the MS cannot usethe corresponding Dedicated Ranging Code. The unit of the Period forDedicated Ranging Code may use second/millisecond of the time, and mayindicate a particular frame for ending the Dedicated Ranging Code usingLeast Significant Bits of the Frame Number.

Through the Scan_Request/Scan_Response message transaction includingthose parameters, the BS or the MS determines which operation isperformed by the MS 510 for the BS 520 in the scanning interval. Forexample, the BS or the MS determines whether to conduct Scanning Only orBoth Scanning and Association.

The Scanning is explained as below (step 2).

The MS 510 fundamentally measures the channel of the DL of the BS 520.Since the beamforming is applied, the coarse beam selection is performedbetween the MS 510 and the BS 520 and the MS 510 measures each DL Txbeam of the BS 520. In so doing, the metric used can be either the RSSIor the CINR. The MS 510 stores the ID and the measurement result of theDL Tx beam (e.g., DL beam ID and measurement result) of the best signalstrength among the measurement results of the DL Tx beams. DuringScanning procedure, the fine beam selection may be performed between theMS 510 and the BS 520. In that case,

-   -   A. the MS performs the coarse beam selection first to find the        best ‘x’ BSs (i.e. X=the number of candidate BSs which has the        best signal strength). Therefore, the MS repeats coarse beam        selection with neighbor BSs, and it selects the best ‘x’ BSs out        of all BSs with which the MS performed coarse beam selection.        The MS performs fine beam selection procedure with the chosen        ‘x’ BSs. Actually, it takes longer time to do fine beam        selection because the number of fine beams is larger than the        number of wide beams. So reducing the number of BSs to do fine        beam selection with. When the MS sends measurement result to the        serving BS after scanning+(optional) association procedure, the        MS can include measurement result of either all BSs or the best        ‘y’ BSs for bine beam    -   B. Unlike A), the MS can directly perform fine beam selection        without 1^(st) step (i.e. selecting ‘x’ BS by coarse beam        selection). Remaining operation is the same as A).

Alternatively, the MS may perform all neighbor BSs without filtering outBSs having weaker signal strength.

The Association is described as below (step 2).

The Association performs the ranging between the MS 510 and the BS 520and the UL coarse beam selection between the MS 510 and the BS 520. Whenthe scanning is performed, the Association can be conducted selectivelyor additionally between the MS 510 and the BS 520. The MS can alsoperform association procedure with only the above mentioned ‘x’ or ‘y’candidate BS. Or, the MS can perform association procedure with the allneighbor BS.

When the Association is activated, the MS 510 can obtain the DedicatedRanging Code to be used per BS using the Scan_Response message. Whenscanning the corresponding BS, the MS 510 additionally sends theDedicated Ranging Code to the corresponding BS. The Ranging Opportunityused may be Contention-based Common Ranging Opportunity available toevery MS for sending the ranging code.

When the Ranging Opportunity is separately set in the Scanning Response,it indicates the Dedicated Ranging Code allocated to the correspondingMS and the dedicated ranging code can be transmitted using the region.The Dedicated Ranging Code includes the best DL Tx beam ID of the BS.Hence, the BS 520 can identify the DL Tx beam to use to send theresponse to the MS 510.

The neighboring BSs 530 and 540 can identify the MS which performs theAssociation based on the Dedicated Ranging Code (theScan_Request/Scan_Response message can be negotiated between the servingBS 520 and the neighboring BSs 530 and 540, which can indicate theRanging Code allocated by the neighboring BSs 530 and 540 to the MS510).

Through the ranging (a sort of the UL coarse beam selection) with the MS510, the BS 520 can obtain the best UL Tx beam of the MS 510 and itsbest UL Rx beam used at this time.

The BS 520 needs to inform the MS 510 of the best UL Tx beam. For doingso, several methods can be used. For example, after completing theranging of the MS 510, the BS 520 can send an RNG-ACK including the ULbeam ID of the best UL beam.

In summary, the MS 510 can obtain the DL Tx beam/DL Rx beam of the BS 20through the scanning and obtain the UL Tx beam/UL Rx beam through theAssociation.

In the Scanning Interleaving Interval, the MS 510 can report theScanning/Association results of the Scanning Duration to the serving BS520. The report can use the Periodic Reporting or the Event-drivenReporting. When the MS reports measurement result, the report messagecan include the measurement result(s) of one BS or more than one BS.

Based on the information, the serving BS 520 can determine handover ofthe MS 510. That is, using the report (Scan_Report, step 3) of the MS510, when determining that the MS 510 requires the handover, the servingBS 520 determine whether to perform the handover by negotiating with thecorresponding BSs about the handover of the corresponding MS based onthe BS measurement information contained in the Scan_Report message ofthe MS 510.

Upon determining the handover, a NW-HO_Request message (step 4-1) and aNW-HO_Response message (step 4-2) are transmitted and received betweenthe serving BS 520 and the neighboring BSs 530 and 540, and the messagescarry the information of the MS.

When the serving BS 520 and the neighboring BSs 530 and 540 negotiateabout the handover, the NW-HO_Request message includes at least thefollowing parameters.

MSID indicates the ID of the MS to hand over.

DL Beam ID is used to indicate the DL Tx beam to be used by thecorresponding neighboring BS to transmit data to the MS after thehandover (Network Re-Entry procedure) of the MS is completed. The DLBeam ID indicates the ID of the DL Tx beam of the greatest signalstrength determined by the MS during the scanning of the correspondingBS.

UL Beam ID is used to indicate the UL Rx beam to be used by thecorresponding neighboring BS to receive data from the MS after thehandover (Network Re-Entry procedure) of the MS is completed. Thisparameter can be included only when the MS performs the Association.

The neighboring BSs 530 and 540 receiving the NW-HO_Request messagerespond to the serving BS 520 with a NW-HO_Response message. TheNW-HO_Response message includes at least the following parameters.

MSID indicates the ID of the MS to hand over. DL Beam Selection is aparameter used to indicate whether the MS applies or omits DL BeamSelection with respect to the corresponding neighboring BS. If timeelapsed by HO procedure is expected to be longer than coherence time(the time duration over which the channel impulse response is consideredto be not varying), this DL Beam Selection will be set to 1. By otherpurpose, this DL Beam Selection may be set to 0 or 1. The elapsed timeimplies time between a) sending report measurement message to theserving BS and b) action time when the MS attaches to target BS.

UL Beam Selection indicates whether to perform UL Beam Selection whenthe MS performs the Network Re-Entry to the corresponding neighboringBS, that is, indicates that the MS needs to perform the ranging (theranging including the UL beam selection). The ranging can be DedicatedRanging or Normal Ranging. The UL Beam Selection of 0 signifies that theMS does not need the UL Beam Selection. This implies that the MS obtainsthe best UL Tx beam through the Association (in connection with the ULbeam ID). That is, when the MS sends the Scan_Report including the ULbeam ID, it is reflected to the NW-HO_Request and reported to theneighboring BS. Based on this, the neighboring BS, upon determining thatthe UL beam selection of the MS is unnecessary, sets the correspondingparameter to zero. Even though the MS has performed UL beam selectionthrough the association procedure, if time elapsed by HO procedure isexpected to longer than coherence time, this UL Beam Selection will beset to 1. By other purpose, this UL Beam Selection may be set to 0 or 1.

When the Dedicated Ranging is set to 1, Action Time is used to notifythe time for using the Dedicated Ranging Code. That is, the Action Timeis used to indicate the time for initiating Network Entry with thecorresponding BS, and the unit can be expressed as the time or the framenumber. Meanwhile, when the DL Beam Selection=0 and the UL BeamSelection=0, the Action Time indicates the actual data transmission andreception time.

When the UL Beam Selection=1, Dedicated Ranging is used for thecorresponding neighboring BS to allocate the Dedicated Ranging Code orthe Dedicated Ranging Opportunity for the fast handover of the MS. Inthis case, the parameter Dedicated Ranging is set to 1. When the UL BeamSelection=1 and the Dedicated Ranging=0, the MS randomly selects theRanging Code and performs the normal ranging because the DedicatedRanging Code is not separately allocated. When the UL Beam Selection=0,the MS omits the ranging with the neighboring Bs and thus this parametercan be omitted.

The Dedicated Ranging Code is included when the Dedicated Ranging=1(with UL Beam Selection=1). This parameter indicates the ranging code tobe used by the MS in the ranging. The BS recognizes the corresponding MSbased on the allocated ranging code.

Period for Dedicated Ranging Code is included when the Dedicated Rangingis set to 1. That is, when the MS performs the handover (the NetworkRe-Entry) to the corresponding BS, the parameter indicates the validtime of the Dedicated Ranging Code to be used by the MS. When this timepasses, the corresponding Dedicated Ranging Code may be allocated toother MS and accordingly the MS may not use the Dedicated Ranging Codeany more. Finally, when this time passes, the MS randomly selects theRanging Code and performs the Network Re-Entry.

Dedicated RACH Pattern ID is included when the Dedicated Ranging=1, andindicates a scheduling pattern index of the Dedicated RACH (RangingOpportunity) allocated by the BS to the corresponding MS. Using theindex, when and where the Dedicated Ranging Opportunity is located canbe obtained. That is, the pattern of Time offset/Opportunitylocation/number/allocation period from the Action Time to the firstRanging Opportunity can be obtained from the index.

Through the NW-HO_Request/Response message transmission and reception(steps 4-1 and 4-2), context sharing/update of the MS 510 is completedbetween the corresponding serving BS 520 and the neighboring BSs 530 and540 (step 5).

Through the handover negotiation with the neighboring BSs 530 and 540,the serving BS 520 can identify the neighboring BSs 530 and 540 forprocessing the handover of the corresponding MS 510 and transacts thehandover messages with the MS 510.

Next, the serving BS 520 sends an Air-HO_Request message to the MS 520(step 6). The Air-HO_Request message includes at least the followingparameters.

BSID(s) indicates the ID of the BS to which the MS hands over. Aplurality of the BSIDs can exist.

DL Beam Selection is the same as the DL Beam Selection of theNW-HO_Response.

UL Beam Selection is the same as the UL Beam Selection of theNW-HO_Response.

Dedicated Ranging is the same as the Dedicated Ranging of theNW-HO_Response.

Action Time is the same as the Action Time of the NW-HO_Response.

Dedicated Ranging Code is the same as the Dedicated Ranging Code of theNW-HO_Response.

Period for Dedicated Ranging Code is the same as the Period forDedicated Ranging Code of the NW-HO_Response.

Dedicated RACH Pattern ID is the same as the Dedicated RACH Pattern IDof the NW-HO_Response.

The MS 510 receiving the Air-HO_Request message sends an Air-HO_Responsemessage to the serving BS 520 in response (step 7).

The Air-HO_Response message includes at least the following parameters.

Confirmation Code indicates whether the MS permits the handover requestof the Air-HO_Request of the BS. That is, when the MS can hand over, theConfirmation Code is set to zero. When the MS cannot hand over, theConfirmation Code is set to 1.

BSID(s) indicates the ID of the BS determining the handover of the MSwhen the Confirmation Code is zero, that is, when the handover isperformed.

Last SN(s) indicates Sequence Number of the last packet successfullyused (transmitted) per service flow of the MS. This parameter exists asmany as the service flows of the MS.

When the Confirmation Code of the Air-HO_Response message is zero, theserving BS 520 receiving the Air-HO_Response from the MS 510 sends aNW-HO_Confirm message to the neighboring BSs 530 and 540 which determineto support the handover of the MS 510 among the neighboring BSs 530 and540 negotiated about the handover of the corresponding MS (step 8). TheNW-HO_Confirm message includes at least the following messages.

MSID indicates the ID of the MS.

BSID indicates the ID of the BS determining the handover of the MS.

Last SN(s) is the same as the Last SN(s) of the Air-HO_Response message.

Of the neighboring BSs 530 and 540 receiving the NW-HO_Confirm message,the neighboring BS 540 without the corresponding BSID can release theresource reserved for the corresponding MS 510 because there is no needto maintain the resource. Since the neighboring BS 530 having thecorresponding BSID determines the handover of the MS 510, it maintainsthe reserved resources and prepares the handover (the Network Re-Entry)of the MS 510.

The corresponding neighboring BS 530 having the BSID of theNW-HO_Confirm message conduct the beam selection with the MS from theframe indicated by the negotiated Action Time (step 9) or initiates theactual DL data transmission (step 10). The operation of the MS differsaccording to the negotiated parameter.

When the DL Beam Selection=0 and the UL Beam Selection=0 in theAir-HO_Request message, this implies that the MS 510 does not need theBeam Selection in the DL/UL. The MS transmits and receives data usingthe corresponding beam from the frame indicated by the Action Time usingthe DL Rx beam (the BS uses the corresponding DL Tx beam based on the DLBeam ID) and the UL Tx beam (the BS uses the corresponding UL Rx beambased on the UL Beam ID) obtained through the Scanning/Association. Thatis, the beam selection is not conducted separately and thus the handoverlatency can be prevented.

When the DL Beam Selection=0 and the UL Beam Selection=1, this impliesthat the MS does not need the DL Beam Selection with the correspondingneighboring BS. The UL Beam Selection=1 signifies that the MS does notperform the Association and requests the UL Beam Selection. When theDedicated Ranging=1, the corresponding neighboring BSs 530 and 540allocate the dedicated resource (Dedicated Ranging Code/DedicatedRanging Opportunity) to the MS 510 and the MS 510 performs the ranging(and the UL beam selection at the same time) using the resource.

When the Dedicated Ranging=0, the BS does not allocate the dedicatedresource to the MS 510 and accordingly the MS 510 performs the normalranging (and the UL beam selection at the same time).

The DL Beam Selection=1 and the UL Beam Selection=1 signify that the MSrequests both of the DL beam selection and the UL beam selection. Sincethe beam information of the MS is old and invalid, it is necessary toselect a new beam.

Hence, similarly to the DL Beam Selection=0 and the UL Beam Selection=1,when the Dedicated Ranging=1, the corresponding neighboring BSs 530 and540 allocate the dedicated resource (Dedicated Ranging Code/DedicatedRanging Opportunity) to the MS 510 and the MS 510 performs the ranging(and the UL beam selection at the same time) using the resource. Bycontrast, when the Dedicated Ranging=0, the BS does not allocate thededicated resource to the MS and thus the MS performs the normal ranging(and the UL beam selection at the same time).

FIG. 6 illustrates a flowchart of operations of the MS according to anexemplary embodiment of the present disclosure.

Referring to FIG. 6, the MS sends the Scan_Request message to theserving BS in step 605, receives the Scan_Response message from theserving BS in step 610, and determines whether and how to perform thescanning and the Association.

In step 615, the MS scans the serving BS and/or the neighboring BS. Whennegotiating about the Association in the Scan_Request/Scan_Responsemessage negotiation in step 620, the MS performs the Association in step625.

Next, the MS reports the scan result to the serving BS in step 630.

The scanning is performed based on the Scan_Request/Scan_Responsemessage negotiation, the MS scans several BSs including the serving BSduring the set time interval, and reports the scan result to the servingBS over the interleaving interval. The Scan_Request/Scan_Responsemessages include the parameter Scanning Type indicating whether toconduct only the Scanning, or both of the Scanning and the Association.The scanning period is determined by the parameter Scanning iteration.That is, the Scanning iteration indicates how many times the scanning isrepeated and how many times (scanning duration+interleaving interval) isiterated. The MS can obtain the Dedicated Ranging Code added by theserving BS to the Scan_Response message and received from theneighboring BS, and use the Dedicated Ranging Code to select the UL beamwith the neighboring BS.

The MS can determine the best DL Tx and Rx beams and UL Tx and Rx beamsof the serving BS and the neighboring BS through the Scanning and theAssociation.

When receiving the Air-HO_Request message from the serving BS in step635, the MS determines whether to conduct the handover, and theneighboring BS for the handover based on the parameters of theAir-HO_Request message in step 640.

In step 645, the MS sends the Air-HO_Response message including theinformation about whether to conduct the handover and the neighboring BSfor the handover, to the serving BS.

The MS performs, if necessary, the UL and/or DL beam selection with thedetermined BS based on the parameters of the Air-HO_Request message instep 650 and exchanges the data in step 655.

FIG. 7 illustrates a flowchart of operations of the serving BS accordingto an exemplary embodiment of the present disclosure.

Referring to FIG. 7, when receiving the Scan_Request message from the MSin step 705, the serving BS sets the parameters for the Scanning or theAssociation and receives the Dedicated Ranging Code of the MS from theneighboring BS in the Association negotiation with the neighboring BS instep 710.

In step 715, the serving BS sends the Scan_Response message includingthe parameters to the MS. Next, the MS performs the Scanning and/or theAssociation.

In step 735, the serving BS receives the Scan_Report from the MS. The BScan determine the best DL Tx and Rx beams and UL Tx and Rx beams to theMS through the Scanning and the Association.

In step 740, the serving BS sends the NW-HO_Request message to theneighboring MS. The NW-HO_Request message includes the MSID, the DL beamID, and the UL beam ID to be used by the MS For the neighboring BS.

When receiving the NW-HO_Response message from the neighboring BS instep 745, the serving BS identifies the BS to which the MS can handover, based on the parameters of the NW-HO_Response message in step 750.

In step 755, the serving BS sends the Air-HO_Request message. TheAir-HO_Request message includes the ID of the BS to which the MS canhand over, and the information about whether the UL and DL beamselections are conducted for the BS.

Upon receiving the Air-HO_Response message from the MS in step 760, theserving BS identifies whether the MS can hand over and the BS for thehandover of the MS in the Air-HO_Response message.

The serving BS sends the NW-HO_Confirm message including a list of BSsallowing the handover of the MS to the neighboring BS which can supportthe handover of the MS in step 765.

FIG. 8 illustrates a flowchart of operations of the neighboring BSaccording to an exemplary embodiment of the present disclosure.

Referring to FIG. 8, as negotiating with the serving BS about theAssociation, the neighboring, BS transmits the Dedicated Ranging Code ofthe corresponding MS to the serving BS in step 805. Later, theneighboring BS, receiving the Dedicated Ranging Code, can identify whichMS performs the Association.

When the Association with the MS is required in step 820, theneighboring BS conducts the Association with the MS in step 825.

When receiving the NW-HO_Request message from the serving BS in step830, the neighboring BS obtains the context information of the MS fromthe NW-HO_Request message and determines whether to support the handoverof the MS and to select the DL/UL beams in step 835. The contextinformation of the MS can include the MSID to be used by the MS for theneighboring BS, the DL beam ID, and the UL beam ID.

In step 840, the neighboring BS transmits to the serving BS theNW-HO_Response message including the information about whether thehandover of the MS is supported and whether the DL/UL beams areselected.

When receiving the NW-HO_Confirm message from the serving BS, theneighboring BS determines whether to reserve the resource for the MSbased on the parameters of the NW-HO_Confirm message, and, if necessary,performs the UL and/or UL beam selection with the MS in step 850.

In step 855, the neighboring BS exchanges data with the MS over the bestUL and DL beams.

FIG. 9 illustrates a block diagram of a transmitting stage according toan exemplary embodiment of the present disclosure. Herein, thetransmitting stage is assumed to adopt digital/analog hybridbeamforming, and can represent a transmitting stage of the MS and theBS.

Referring to FIG. 9, the transmitting stage includes K-ary channelencoders 900-1 through 900-K, a Multiple Input Multiple Output (MIMO)encoder 910, a precoder 920, N_(T)-ary Radio Frequency (RF) paths 930-1through 930-N_(T), N_(T)-ary antennas 950-1 through 950-N_(T), a beamsetter 960, and a controller 970.

The K-ary channel encoders 900-1 through 900-K each include a channelencoder and a modulator for encoding, modulating, and outputting thesignal to transmit to a receiving stage.

The MIMO encoder 910 multiplexes the modulated signals fed from theK-ary channel encoders 900-1 through 900-K, to signals to transmitthrough N_(T)-ary streams in order to send them over the N_(T)-aryantennas 950-1 through 950-N_(T).

The precoder 920 precodes the N_(T)-ary signals fed from the MIMOencoder 910 to precodes for the digital beamforming and provides theprecodes to the RF paths 930-1 through 930-N_(T) respectively.

The N_(T)-ary RF paths 930-1 through 930-N_(T) each process the signalsfed from the precoder 920 in order to output the signals through thecorresponding antennas 950-1 through 950-N_(T). In so doing, theN_(T)-ary RF paths 930-1 through 930-N_(T) are constructed identically.Thus, the first RF path 930-1 is explained mainly here. The otherN_(T)-ary RF paths 930-2 through 930-N_(T) are constructed the same asthe first RF path 930-1.

The first RF path 930-1 includes N_(A)-ary modulators 932-11 through932-1N_(A), an analog beamformer 990, and N_(A)-ary power amplifiers940-11 through 940-1N_(A). Herein, the N_(A) denotes the number ofantenna elements constituting the first antenna 950-1.

The N_(A)-ary modulators 932-11 through 932-1N_(A) each modulate andoutput the signal fed from the precoder 920 according to a communicationscheme. For example, the N_(A)-ary modulators 932-11 through 932-1N_(A)each include an Inverse Fast Fourier Transform (IFFT) operator and aDigital to Analog Converter (DAC). The IFFT operator converts the signaloutput from the precoder 920 to a time-domain signal using IFFT. The DACconverts the time-domain signal output from the IFFT operator to ananalog signal.

The analog beamformer 990 changes and outputs the Tx beam direction ofthe N_(A)-ary transmit signals output from the N_(A)-ary modulators932-11 through 932-1N_(A) according to the control signal indicating theTx beam direction provided from the beam setter 960.

For example, the analog beamformer 990 includes a plurality of phaseshifters 934-11 through 934-1N_(A) and 936-11 through 936-1N_(A), andcombiners 938-11 through 938-1N_(A). The N_(A)-ary modulators 932-11through 932-1N_(A) each split the output signal to N_(A)-ary signals andoutput them to the respective phase shifters 934-11 through 934-1N_(A)and 936-11 through 936-1N_(A). The phase shifters 934-11 through934-1N_(A) and 936-11 through 936-1N_(A) change the phase of the signalsoutput from the N_(A)-ary modulators 932-11 through 932-1N_(A) accordingto the control signal indicating the Tx beam direction provided from thebeam setter 960. The combiners 938-11 through 938-1N_(A) combine theoutput signals of the phase shifters 934-11 through 934-1N_(A) and936-11 through 936-1N_(A) corresponding to the antenna elements.

The power amplifiers 940-11 through 940-1N_(A) each amplify the power ofthe signal output from the combiners 938-11 through 938-1N_(A) andoutput the amplified signal to the outside through the first antenna950-1.

The beam setter 960 selects the Tx beam direction to be used to transmitthe signal, and provides the control signal according to the selected Txbeam direction to the analog beamformer 990 under control of thecontroller 970.

For example, the beam setter 960 provides the control signal accordingto the Tx beam direction for carrying the reference signal, thepreamble/midamble, or the data, to the analog beamformer 990 under thecontrol of the controller 970.

For example, the beam setter 960 selects the Tx beam direction forattaining the optimal transmission efficiency with the receiving stageby considering the channel information of the Tx beam directionsprovided from the MS under the control of the controller 970.

The controller 970 controls the beam setter 960 to select the Tx beamdirection. For example, the controller 970 controls the beam setter 960to send the reference signal or the data in the Tx beam directionssupported by the transmitting stage. For example, the controller 970controls the beam setter 960 to select the optimal Tx beam direction bytaking into account the channel information of the Tx beam directionprovided from the receiving stage.

The transmitting stage may receive the optimal Tx beam directionselected by the receiving stage, from the receiving stage. In this case,the beam setter 960 provides the analog beamformer 990 with the controlsignal and the data according to the optimal Tx beam direction selectedby the receiving stage.

The controller 970 of the transmitting stage can send a control messageto the opponent node (e.g., the serving BS, the neighboring BS, or theMS).

FIG. 10 illustrates a block diagram of the receiving stage according toan exemplary embodiment of the present disclosure. Herein, the receivingstage is assumed to adopt the digital/analog hybrid beamforming, and canrepresent a receiving stage of the MS and the BS.

As shown in FIG. 10, the receiving stage includes N_(R)-ary antennas1000-1 through 1000-N_(R), N_(R)-ary RF paths 1010-1 through 1010-N_(R),a postprocessor 1020, a MIMO decoder 1030, T-ary channel decoders 1040-1through 1040-T, a channel estimator 1050, a controller 1060, and a beamsetter 1070.

The N_(R)-ary RF paths 1010-1 through 1010-N_(R) process the signalsreceived via the corresponding antennas 1000-1 through 1000-N_(R). TheN_(R)-ary RF paths 1010-1 through 1010-N_(R) are constructedidentically. Accordingly, the structure of the first RF path 1010-1 ismainly described. The other RF paths 1010-2 through 1010-N_(R) areconstructed the same as the first RF path 1010-1.

The first RF path 1010-1 includes an analog beamformer 1080 andN_(B)-ary demodulators 1018-11 through 1018-1N_(B). Herein, the N_(B)denotes the number of antenna elements constituting the first antenna1000-1.

The analog beamformer 1080 alters and outputs the direction of theN_(B)-ary receive signals output from the antenna elements of the firstantenna 1000-1 according to the Tx beam direction provided from the beamsetter 1070. For example, the analog beamformer 1080 includes aplurality of phase shifters 1012-11 through 1012-1N_(B) and 1014-11through 1014-1N_(B), and combiners 1016-11 through 1016-1N_(B). Theantenna elements of the first antenna 1000-1 split the receive signal toN_(B)-ary signals and output them to the respective phase shifters1012-11 through 1012-1N_(B) and 1014-11 through 1014-1N_(B). The phaseshifters 1012-11 through 1012-1N_(B) and 1014-11 through 1014-1N_(B)change the phase of the signals output from the antenna elements of thefirst antenna 1000-1 according to the Rx beam direction provided fromthe beam setter 1070. The combiners 1016-11 through 1016-1N_(B) combinethe output signals of the phase shifters 1012-11 through 1012-1N_(B) and1014-11 through 1014-1N_(B) corresponding to the antenna elements.

The N_(B)-ary demodulators 1018-11 through 1018-1N_(B) demodulate andoutput the received signals fed from the combiners 1016-11 through1016-1N_(B) according to the communication scheme. For example, theN_(B)-ary demodulators 1018-11 through 1018-1N_(B) each include anAnalog to Digital Converter (ADC) and a FFT operator. The ADC convertsthe receive signal fed from the combiners 1016-11 through 1016-1N_(B) toa digital signal. The FFT operator converts the signal fed from the ADCto a frequency-domain signal using FFT.

The postprocessor 1020 post-decodes the signals fed from the N_(R)-aryRF paths 1010-1 through 1010-N_(R) according to the precoding scheme ofthe transmitting stage, and provides the post-decoded signals to theMIMO decoder 1030.

The MIMO decoder 1030 multiplexes the N_(R)-ary receive signals outputfrom the postprocessor 1020 to T-ary signals so that the T-ary channeldecoders 1040-1 through 1040-T can decode the signals.

The T-ary channel decoders 1040-1 through 1040-T each include ademodulator and a channel decoder for demodulating and decoding thesignal received from the transmitting stage.

The channel estimator 1050 estimates the channel information based onthe reference signal transmitted from the transmitting stage in the Txbeam directions. When a scan event occurs, the channel estimator 1050estimates the channel information of each Tx beam direction. Herein, thechannel information includes at least one of the SNR, the CINR, and theRSSI.

The controller 1060 transmits the channel information of the Tx beamdirections estimated by the channel estimator 1050, to the transmittingstage. For example, the controller 1060 transmits the channelinformation of the Tx beam directions of good channels status, to thetransmitting stage.

For example, when the receiving stage supports the Rx beamforming, thecontroller 1060 can transmits the channel information of the Tx beamdirections having the channel status per Rx beam direction exceeding areference value, to the transmitting stage.

The controller 1060 may select the Tx beam direction for attaining theoptimal transmission efficiency with the transmitting stage, byconsidering the channel information of the Tx beam directions estimatedby the channel estimator 1050.

For example, the controller 1060 selects the Tx beam direction forattaining the optimal transmission efficiency with the transmittingstage, by considering the channel information of the Tx beam directionsestimated by the channel estimator 1050.

When the transmitting stage and the receiving stage belong to the MS,they operate as follows.

The MS can confirm the Scanning or the Association by sending andreceiving the Scan_Request/Scan_Response messages, carry out theScanning or the Association, and send the result to the serving BS.

The MS determines the neighboring BS for the handover based on theparameters of the Air-HO_Request message and sends the result to theserving BS.

The MS can selectively perform the DL/UL beam selection for the handoverBS based on the parameters of the Air-HO_Request message.

When the transmitting stage and the receiving stage belong to the BS,they operate as follows.

The serving BS determines whether to perform the Scanning or theAssociation of the MS by sending and receiving theScan_Request/Scan_Response messages. The serving BS can receive the MSDedicated Ranging Code from the neighboring BS.

The serving BS can identify the BS for supporting the handover of the MSby sending the NW-HO_Request message to the neighboring BS, and informthe MS of the BS supporting the MS handover using the Air-HO_Requestmessage.

The serving BS, upon receiving the NW-HO_Response from the MS, canidentify the BS to which the MS hands over and inform the neighboring BSwhether the neighboring BS is the MS handover target BS.

When the transmitting stage and the receiving stage belong to theneighboring BS, the controller 970 operates as follows.

The neighboring BS sends the Dedicated Ranging Code of the MS to theserving BS. The neighboring BS can inform the serving BS whether thehandover of the MS supported or not, by sending and receiving theNW-HO_Request message/NW-HO_Response message.

The neighboring BS can confirm the handover target BS of the MS based onthe NW-HO_Confirm message, and prepare the handover of the MS.

The controller can function as the beam setter in FIGS. 9 and 10.

As set forth above, the beam selection is conducted in the scanninginterval in advance, and the beam selection is omitted in the process ofthe handover using the stored DL/UL beam information. Therefore, thehandover latency increase caused by the beam selection can be minimized.

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method for handover in a Mobile Station (MS) ofa wireless communication system which adjusts a beam direction, themethod comprising: sending a scan request message for scanning adownlink (DL) beam or a DL beam and uplink (UL) beam with respect to aserving base station (BS) and a neighboring BS, to the serving BS;receiving a scan response message; determining the DL beam or the DLbeam and UL beam for the MS by performing scanning or the scanning andassociation with the serving BS and the neighboring BS based on the scanresponse message; sending a scan report message comprising a result ofthe scanning or the scanning and the association to the serving BS; whenreceiving an air handover (HO) request message from the serving BS,generating an air-HO response message comprising information of aneighboring handover BS to which the MS hands over based on the air-HOrequest message; performing beam selection with the neighboring handoverBS based on the air-HO request message; and performing handover, andtransmitting and receiving data to and from the neighboring handover BS.2. The method of claim 1, wherein the scan request and scan responsemessages comprise at least one of scanning type indicating whether thescanning only is performed or and the scanning and the association bothare performed, scanning iteration indicating how many times the scanningwhich comprises scanning duration indicating a scanning interval and aninterleaving interval between the scanning durations is repeated,scanning metric indicating a measurement metric of the scanning,scanning report type indicating a scanning report type comprisingperiodic reporting or event-driven reporting in case of an event, reportperiod indicating a report period when the scanning reporting type isset to the Periodic reporting, report condition indicating a reportcondition when the scanning reporting type is set to the Event-drivenReporting, a base station identifier (BSID) indicating an identifier ofa BS, dedicated ranging code to be used by the MS in the BS having theBSID in the process of the association, dedicated ranging opportunityindicating an opportunity of the MS for transmitting the dedicatedranging code, and period for dedicated ranging code indicating a validtime of the ranging rode.
 3. The method of claim 1, wherein performingthe scanning comprises performing coarse beam selection, or the coarsebeam selection and fine beam selection between the MS and the serving BSor between the MS and the neighboring BS, storing a result, anddetermining the DL Tx beam and the DL Rx beam.
 4. The method of claim 1,wherein performing the association comprises performing ranging betweenthe MS and the serving BS or between the MS and the neighboring BS,stores a result by performing UL coarse beam selection, and determiningthe UL Tx beam of the MS or the UL Rx beam of the serving BS or theneighboring BS.
 5. The method of claim 1, wherein the air-HO requestmessage comprises at least one of at least one base station identifier(BSID) indicating an identifier of the neighboring handover BS to whichthe MS hands over, DL beam selection indicating whether the MS performsthe DL beam selection on the corresponding neighboring BS, UL beamselection indicating whether to perform the UL beam selection when theMS hands over to the corresponding neighboring BS, dedicated rangingused when the UL beam selection is set and the corresponding neighboringBS allocates a dedicated ranging code or a dedicated ranging opportunityfor fast handover of the MS, action time indicating a time for using thededicated ranging code when the dedicated ranging is set, and indicatinga time for transmitting and receiving actual data when the DL beamselection is not set and the UL beam selection is not set, dedicatedranging code contained when the dedicated ranging is set, period fordedicated ranging code contained when the dedicated ranging is set andindicating a valid time of the dedicated ranging code to be used by theMS, and dedicated random access channel (RACH) Pattern identifierindicating an index of a scheduling pattern of dedicated RACH rangingopportunity allocated by the BS to the corresponding MS when thededicated ranging is set.
 6. The method of claim 1, wherein the air-HOresponse message comprises at least one of confirmation code indicatingwhether to permit a handover request using the air-HO request of the BS,base station identifiers (BSIDs) indicating an identifier of at leastone BS which determines the handover of the MS, and last sequencenumbers (SNs) indicating a sequence number of a last packet successfullyused per service flow of the MS and provided as many as the serviceflows of the MS.
 7. The method of claim 1, wherein performing the beamselection with the neighboring BS of the handover comprises: selecting abeam with the BS determined for the handover according to a parameter ofthe air-HO request message.
 8. A method for handover in a serving BaseStation (BS) of a wireless communication system which adjusts a beamdirection, the method comprising: receiving a Scan_Request message forscanning a downlink (DL) beam or a DL beam and uplink (UL) beam for amobile station (MS), from the MS, receiving a dedicated ranging code ofthe MS from a neighboring BS through negotiation with the neighboringBS; sending a scan response message comprising information about whetherto perform scanning or the scanning and association, to the MS;receiving from the MS a scan report message comprising information ofthe DL beam or the DL beam and UL beam for the MS and a result of thescanning or the scanning and the association; sending a network handover(NW-HO) request message to at least one neighboring BS based on the scanresponse message in order to identify a BS capable of supportinghandover of the MS and to share context of the MS; receiving a NW-HOresponse message comprising information indicating whether the handoverof the MS is supportable, from the at least one neighboring BS; sendingan air-HO request message to the MS based on the NW-HO response message,and receiving an air-HO response message comprising informationindicating whether the MS is able to hand over and information of atleast one neighboring BS to which the MS hands over; and sending a NW-HOconfirm message informing whether the handover of the MS is performed,to the neighboring BS which sends the NW-HO request message based on theair-HO response message.
 9. The method of claim 8, wherein the scanrequest and scan response messages comprise at least one of scanningtype indicating whether the scanning only is performed or and thescanning and the association both are performed, scanning iterationindicating how many times the scanning which comprises scanning durationindicating a scanning interval and an interleaving interval between thescanning durations is repeated, scanning metric indicating a measurementmetric of the scanning, scanning report type indicating a scanningreport type comprising periodic reporting or event-driven reporting incase of an event, report period indicating a report period when thescanning reporting type is set to the periodic reporting, reportcondition indicating a report condition when the scanning reporting typeis set to the event-driven reporting, a base station identifier (BSID)indicating an identifier of a BS, dedicated ranging code to be used bythe MS in the BS having the BSID in the process of the association,dedicated ranging opportunity indicating an opportunity of the MS fortransmitting the dedicated ranging code, and period for dedicatedranging code indicating a valid time of the ranging code.
 10. The methodof claim 8, wherein performing the scanning comprises performing coarsebeam selection, or the coarse beam selection and fine beam selectionbetween the MS and the serving BS or between the MS and the neighboringBS, storing a result, and determining the DL Tx beam and the DL Rx beam.11. The method of claim 8, wherein performing the association comprisesperforming ranging between the MS and the serving BS or between the MSand the neighboring BS, storing a result by performing UL coarse beamselection, and determining the UL Tx beam of the MS or the UL Rx beam ofthe serving BS or the neighboring BS.
 12. The method of claim 8, whereinthe NW-HO request message comprises at least one of a mobile stationidentifier (MSID) indicating an identifier of the MS to hand over, DLbeam identifier indicating the DL Tx beam to be used by the neighboringBS to transmit data to the MS after the handover of the MS is completed,and UL Beam identifier indicating the UL Rx beam to be used by theneighboring BS to receive data from the MS after the handover of the MSis completed, wherein the UL Beam identifier is contained when the MSand the neighboring BS perform the association.
 13. The method of claim8, wherein the NW-HO response message comprises at least one of a mobilestation identifier (MSID) indicating an identifier of the MS to handover, DL beam selection indicating whether the MS performs DL beamselection for the neighboring BS, UL beam selection indicating whetherto perform UL beam selection when the MS hands over to the neighboringBS, dedicated ranging used when the UL beam selection is set and thecorresponding neighboring BS allocates a dedicated ranging code or adedicated ranging opportunity for fast handover of the MS, action timeindicating a time for using the dedicated ranging code when thededicated ranging is set, and indicating a time for transmitting andreceiving actual data when the DL beam selection is not set and the ULbeam selection is not set, dedicated ranging code contained when thededicated ranging is set, period for dedicated ranging code containedwhen the dedicated ranging is set and indicating a valid time of thededicated ranging code to be used by the MS, and dedicated random accesschannel (RACH) pattern identifier indicating an index of a schedulingpattern of dedicated RACH ranging opportunity allocated by the BS to thecorresponding MS when the dedicated ranging is set.
 14. The method ofclaim 8, wherein the air-HO_Request message comprises at least one of atleast one base station identifier (BSID) indicating an identifier of theneighboring BS to which the MS hands over, DL beam selection indicatingwhether the MS performs the DL beam selection on the correspondingneighboring BS, UL beam selection indicating whether to perform the ULbeam selection when the MS hands over to the corresponding neighboringBS, dedicated ranging used when the UL beam selection is set and thecorresponding neighboring BS allocates a dedicated ranging code or adedicated ranging opportunity for fast handover of the MS, action timeindicating a time for using the dedicated ranging code when thededicated ranging is set, and indicating a time for transmitting andreceiving actual data when the DL beam selection is not set and the ULbeam selection is not set, dedicated ranging code contained when thededicated ranging is set, period for dedicated ranging code containedwhen the dedicated ranging is set and indicating a valid time of thededicated ranging code to be used by the MS, and dedicated random accesschannel (RACH) pattern identifier indicating an index of a schedulingpattern of dedicated RACH ranging opportunity allocated by the BS to theMS when the dedicated ranging is set.
 15. The method of claim 8, whereinthe air-HO response message comprises at least one of confirmation codeindicating whether to permit a handover request using the air-HO requestof the BS, base station identifiers (BSIDs) indicating an identifier ofat least one BS which determines the handover of the MS, and lastsequence numbers (SNs) indicating a sequence number of a last packetsuccessfully used per service flow of the MS and provided as many as theservice flows of the MS.
 16. The method of claim 8, wherein the NW-HOconfirm message comprises at least one of a mobile station identifier(MSID) indicating an identifier of the MS, a base station identifier(BSID) indicating an identifier of the neighboring BS which the MSdetermines to hand over to, and last sequence numbers (SNs) indicating asequence number of a last packet successfully used per service flow ofthe MS and provided as many as the service flows of the MS.
 17. A methodfor handover in a neighboring base station (BS) of a wirelesscommunication system which adjusts a beam direction, the methodcomprising: sending a dedicated ranging code of a mobile station (MS) toa serving BS through negotiation with the serving BS; performingassociation with the MS to scan a downlink (DL) beam or DL beam anduplink (UL) beam for the MS; receiving from the serving BS a networkhandover (NW-HO) request message based on a scan response messagecomprising a result of scanning or the scanning and association of theMS in order to identify a BS capable of supporting handover of the MSand to share context of the MS; generating and sending a NW-HO responsemessage comprising information indicating whether the handover of the MSis supportable, to the serving BS; receiving from the serving BS a NW-HOconfirm message informing whether the handover of the MS is performed,to the neighboring BS which sends the NW-HO request message based on theair-HO response message; performing beam selection with the MS based onthe NW-HO confirm message; and transmitting and receiving data to andfrom the MS which hands over.
 18. The method of claim 17, whereinperforming the scanning comprises performing coarse beam selection, orthe coarse beam selection and fine beam selection between the MS and theserving BS or between the MS and the neighboring BS, storing a result,and determining the DL Tx beam and the DL Rx beam.
 19. The method ofclaim 17, wherein performing the association performing ranging betweenthe MS and the serving BS or between the MS and the neighboring BS,storing a result by performing UL coarse beam selection, and determiningthe UL Tx beam of the MS or the UL Rx beam of the serving BS or theneighboring BS.
 20. The method of claim 17, wherein the NW-HO requestmessage comprises at least one of mobile station identifier indicatingan identifier of the MS to hand over, DL beam identifier indicating theDL Tx beam to be used by the neighboring BS to transmit data to the MSafter the handover of the MS is completed, and UL beam identifierindicating the UL Rx beam to be used by the corresponding neighboring BSto receive data from the MS after the handover of the MS is completed,wherein the handover of the MS is a network re-entry, wherein the ULbeam identifier is contained when the MS and the BS perform theassociation.
 21. The method of claim 17, wherein the NW-HO responsemessage comprises at least one of a mobile station identifier indicatingthe identifier of the MS to hand over, DL beam selection indicatingwhether the MS performs DL beam selection for the neighboring BS, ULbeam selection indicating whether to perform UL beam selection when theMS hands over to the neighboring BS, dedicated ranging used when the ULbeam selection is set and the neighboring BS allocates a dedicatedranging code or a dedicated ranging opportunity for fast handover of theMS, action time indicating a time for using the dedicated ranging codewhen the dedicated ranging is set, and indicating a time fortransmitting and receiving actual data when the DL beam selection is notset and the UL beam selection is not set, dedicated ranging codecontained when the dedicated ranging is set, period for dedicatedranging code contained when the dedicated ranging is set and indicatinga valid time of the dedicated ranging code to be used by the MS, anddedicated random access channel pattern identifier indicating an indexof a scheduling pattern of dedicated random access channel rangingopportunity allocated by the BS to the corresponding MS when thededicated ranging is set.
 22. The method of claim 17, wherein the NW-HOconfirm message comprises at least one of mobile station identifierindicating the identifier of the MS, base station identifier indicatingthe identifier of the BS which the MS determines to hand over to, andlast sequence number (SNs) indicating a sequence number of a last packetsuccessfully used per service flow of the MS and provided as many asservice flows of the MS.
 23. An apparatus of a mobile station (MS) forhandover in a wireless communication system which adjusts a beamdirection, the apparatus comprising: a receiver configured to receive atleast one reference signal from a base station (BS) in at least onedownlink (DL) Tx beam direction; a transmitter configured to send aranging signal to the BS in at least one uplink (UL) Tx beam direction;a channel estimator configured to estimate a channel according to the atleast one DL Tx beam direction using the at least one reference signal;and a controller configured to select DL and UL beams between the BS andthe MS by considering channel information according to the at least oneDL Tx beam direction, and control to send and receive messages to andfrom the BS.
 24. The apparatus of claim 23, wherein the controller isconfigured to control to send a scan request message for scanning the DLbeam or the DL beam and UL beam with respect to a serving BS and aneighboring BS, to the serving BS, to receive a scan response message,to determine the DL beam or the DL beam and UL beam for the MS byperforming scanning or scanning and association with the serving BS andthe neighboring BS based on the scan response message, to send a scanreport message comprising a result of the scanning or the scanning andthe association to the serving BS, to generate, when receiving an airhandover (HO) request message from the serving BS, an air-HO responsemessage comprising information of a neighboring BS to which the MS handsover, based on the air-HO request message, to perform beam selectionwith the neighboring BS of the handover based on the air-HO requestmessage, to perform the handover, and to transmit and receive data toand from the neighboring BS of the handover.
 25. The apparatus of claim24, wherein the scan request and scan response messages comprise atleast one of scanning type indicating whether the scanning only isperformed or and the scanning and the association both are performed,scanning iteration indicating how many times the scanning whichcomprises scanning duration indicating a scanning interval and aninterleaving interval between the scanning durations is repeated,scanning metric indicating a measurement metric of the scanning,scanning report type indicating a scanning report type comprisingperiodic reporting or event-driven reporting in case of an event, reportperiod indicating a report period when the scanning reporting type isset to the periodic reporting, report condition indicating a reportcondition when the scanning reporting type is set to the event-drivenreporting, base station identifier indicating an identifier of the BS,dedicated ranging code to be used by the MS in the BS having the basestation identifier in the process of the association, dedicated rangingopportunity indicating an opportunity of the MS for transmitting thededicated ranging code, and Period for dedicated ranging code indicatinga valid time of the ranging code.
 26. The apparatus of claim 24, whereinthe controller is configured to control to perform coarse beamselection, or the coarse beam selection and fine beam selection betweenthe MS and the serving BS or between the MS and the neighboring BS,store a result, and determine the DL Tx beam and the DL Rx beam.
 27. Theapparatus of claim 24, wherein the controller is configured to controlto perform ranging between the MS and the serving BS or between the MSand the neighboring BS, store a result by performing UL coarse beamselection, and determine the UL Tx beam of the MS or the UL Rx beam ofthe serving BS or the neighboring BS.
 28. The apparatus of claim 24,wherein the air-HO request message comprises at least one of at leastone base station identifier indicating the identifier of the BS to whichthe MS hands over, DL beam selection indicating whether the MS performsthe DL beam selection on the corresponding neighboring BS, UL beamselection indicating whether to perform the UL beam selection when theMS hands over to the corresponding neighboring BS, dedicated rangingused when the UL beam selection is set and the corresponding neighboringBS allocates a dedicated ranging code or a dedicated ranging opportunityfor fast handover of the MS, an action time indicating a time for usingthe dedicated ranging code when the dedicated ranging is set, andindicating a time for transmitting and receiving actual data when the DLbeam selection is not set and the UL beam selection is not set,dedicated ranging code contained when the dedicated ranging is set,Period for dedicated ranging code contained when the dedicated rangingis set and indicating a valid time of the dedicated ranging code to beused by the MS, and dedicated random access channel pattern identifierindicating an index of a scheduling pattern of dedicated random accesschannel ranging opportunity allocated by the BS to the corresponding MSwhen the dedicated ranging is set.
 29. The apparatus of claim 24,wherein the air-HO response message comprises at least one ofconfirmation code indicating whether to permit a handover request usingthe air-HO request of the BS, base station identifier(s) indicating theidentifier of at least one BS which determines the handover of the MS,and last sequence numbers (SNs) indicating a sequence number of a lastpacket successfully used per service flow of the MS and provided as manyas the service flows of the MS.
 30. The apparatus of claim 24, wherein,when performing the beam selection with the neighboring BS of thehandover, the controller is configured to select a beam with the BSdetermined for the handover, according to a parameter of the air-HOrequest message.
 31. An apparatus of a serving base station (BS) forhandover in a wireless communication system which adjusts a beamdirection, the apparatus comprising: at least one antenna comprising aplurality of antenna elements; a transmitter configured to send at leastone reference signal in at least one downlink (DL) Tx beam direction; areceiver configured to receive channel information according to at leastone uplink (UL) Tx beam direction from a mobile station (MS); acontroller configured to select the UL Tx beam direction by consideringthe channel information according to at least one uplink (UL) Tx beamdirection received from the MS through the receiver, select DL beam andUL beam between the MS and the serving BS by sending and receivingmessages for the MS in consideration of the selected UL Tx beamdirection, and provide information for handover to the MS; and aplurality of Radio Frequency (RF) paths connected to the respectiveantenna elements, and configured to form a beam to send a signal to theMS according to the DL Tx beam direction selected by the controller. 32.The apparatus of claim 31, wherein the controller is configured toreceive a scan request message for scanning the DL beam or the DL beamand UL beam with respect to the MS, from the MS, receive a dedicatedranging code of the MS from a neighboring BS through negotiation withthe neighboring BS, send a scan response message comprising informationabout whether to perform scanning or the scanning and association, tothe MS, receive from the MS a scan report message comprising informationof the DL beam or the DL beam and UL beam for the MS and a result of thescanning or the scanning and the association, sends a network-handover(NW-HO) request message to at least one neighboring BS based on the scanresponse message in order to identify a BS capable of supportinghandover of the MS and to share context of the MS, receives a NW-HOresponse message comprising information indicating whether the handoverof the MS is supportable, from the at least one neighboring BS, send anair-HO request message to the MS based on the NW-HO response message,receive an air-HO response message comprising information indicatingwhether the MS is able to hand over and information of at least oneneighboring BS to which the MS hands over, and send a NW-HO confirmmessage informing whether the handover of the MS is performed, to theneighboring BS which sends the NW-HO request message based on the air-HOresponse message.
 33. The apparatus of claim 32, wherein the scanrequest and scan response messages comprise at least one of scanningtype indicating whether the scanning only is performed or and thescanning and the association both are performed, scanning iterationindicating how many times the scanning which comprises scanning durationindicating a scanning interval and an interleaving interval between thescanning durations is repeated, scanning metric indicating a measurementmetric of the scanning, scanning report type indicating a scanningreport type comprising periodic reporting or event-driven reporting incase of an event, report period indicating a report period when thescanning reporting type is set to the periodic reporting, reportcondition indicating a report condition when the scanning reporting typeis set to the event-driven reporting, base station identifier indicatingan identifier of the BS, dedicated ranging code to be used by the MS inthe BS having the base station identifier in the process of theassociation, dedicated ranging opportunity indicating an opportunity ofthe MS for transmitting the dedicated ranging code, and period fordedicated ranging code indicating a valid time of the ranging code. 34.The apparatus of claim 32, wherein the controller is configured tocontrol to perform coarse beam selection, or the coarse beam selectionand fine beam selection between the MS and the serving BS or between theMS and the neighboring BS, store a result, and determine the DL Tx beamand the DL Rx beam.
 35. The apparatus of claim 32, wherein thecontroller is configured to control to perform ranging between the MSand the serving BS or between the MS and the neighboring BS, stores aresult by performing UL coarse beam selection, and determine the UL Txbeam of the MS or the UL Rx beam of the serving BS or the neighboringBS.
 36. The apparatus of claim 32, wherein the NW-HO request messagecomprises at least one of mobile station identifier indicating anidentifier of the MS to hand over, DL beam identifier indicating the DLTx beam to be used by the neighboring BS to transmit data to the MSafter the handover of the MS is completed, and UL beam identifierindicating the UL Rx beam to be used by the neighboring BS to receivedata from the MS after the handover of the MS is completed, wherein theUL beam identifier is contained when the MS and the corresponding BSperform the association.
 37. The apparatus of claim 32, wherein theNW-HO response message comprises at least one of mobile stationidentifier indicating the identifier of the MS to hand over, DL beamselection indicating whether the MS performs DL beam selection for thecorresponding neighboring BS, UL beam selection indicating whether toperform UL beam selection when the MS hands over to the correspondingneighboring BS, dedicated ranging used when the UL beam selection is setand the corresponding neighboring BS allocates a dedicated ranging codeor a dedicated ranging opportunity for fast handover of the MS, actiontime indicating a time for using the dedicated ranging code when thededicated ranging is set, and indicating a time for transmitting andreceiving actual data when the DL beam selection is not set and the ULbeam selection is not set, dedicated ranging code contained when thededicated ranging is set, Period for dedicated ranging code containedwhen the dedicated ranging is set and indicating a valid time of thededicated ranging code to be used by the MS, and dedicated random accesschannel pattern identifier indicating an index of a scheduling patternof dedicated random access channel ranging opportunity allocated by theBS to the corresponding MS when the dedicated ranging is set.
 38. Theapparatus of claim 32, wherein the air-HO request message comprises atleast one of at least one base station identifier indicating theidentifier of the BS to which the MS hands over, DL beam selectionindicating whether the MS performs the DL beam selection on thecorresponding neighboring BS, UL beam selection indicating whether toperform the UL beam selection when the MS hands over to thecorresponding neighboring BS, dedicated ranging used when the UL beamselection is set and the corresponding neighboring BS allocates adedicated ranging code or a dedicated ranging opportunity for fasthandover of the MS, action time indicating a time for using thededicated ranging code when the dedicated ranging is set, and indicatinga time for transmitting and receiving actual data when the DL beamselection is not set and the UL beam selection is not set, dedicatedranging code contained when the dedicated ranging is set, Period fordedicated ranging code contained when the dedicated ranging is set andindicating a valid time of the dedicated ranging code to be used by theMS, and dedicated random access channel pattern identifier indicating anindex of a scheduling pattern of dedicated random access channel rangingopportunity allocated by the BS to the corresponding MS when thededicated ranging is set.
 39. The apparatus of claim 32, wherein theair-HO response message comprises at least one of confirmation codeindicating whether to permit a handover request using the air-HO requestof the BS, base station identifier(s) indicating the identifier of atleast one BS which determines the handover of the MS, and last sequencenumbers (SNs) indicating a sequence number of a last packet successfullyused per service flow of the MS and provided as many as the serviceflows of the MS.
 40. The apparatus of claim 32, wherein the NW-HOconfirm message comprises at least one of mobile station identifierindicating the identifier of the MS, base station identifier indicatingthe identifier of the BS which the MS determines to hand over to, andlast sequence number (SNs) indicating a sequence number of a last packetsuccessfully used per service flow of the MS and provided as many as theservice flows of the MS.
 41. An apparatus of a neighboring base station(BS) for handover in a wireless communication system which adjusts abeam direction, the apparatus comprising: at least one antennacomprising a plurality of antenna elements; a transmitter configured tosend at least one reference signal in at least one downlink (DL) Tx beamdirection; a receiver configured to receive channel informationaccording to at least one uplink (UL) Tx beam direction from a mobilestation (MS); a controller configured to select the UL Tx beam directionby considering the channel information according to at least one UL Txbeam direction received from the MS through the receiver, select DL beamand UL beam between the MS and the serving BS by sending and receivingmessages for the MS in consideration of the selected UL Tx beamdirection, and provide information for handover to the serving BS; and aplurality of Radio Frequency (RF) paths connected to the respectiveantenna elements, and configured to form a beam to send a signal to theMS according to the DL Tx beam direction selected by the controller. 42.The apparatus of claim 41, wherein the controller is configured to senda dedicated ranging code of the MS to the serving BS through negotiationwith the serving BS, perform association with the MS to scan the DL beamor the DL beam and UL beam for the MS, receive from the serving BS aNW-HO request message based on a scan response message comprising aresult of scanning or the scanning and association of the MS in order toidentify a BS capable of supporting handover of the MS and to sharecontext of the MS, generate and send a NW-HO response message comprisinginformation indicating whether handover of the MS is supportable, to theserving BS, receive from the serving BS a NW-HO confirm messageinforming whether the handover of the MS is performed, to theneighboring BS which sends the NW-HO request message based on the air-HOresponse message, perform beam selection with the MS based on the NW-HOconfirm message, and transmit and receive data to and from the MS whichhands over.
 43. The apparatus of claim 42, wherein the controller isconfigured to control to perform coarse beam selection, or the coarsebeam selection and fine beam selection between the MS and the serving BSor between the MS and the neighboring BS, store a result, and determinethe DL Tx beam and the DL Rx beam.
 44. The apparatus of claim 42,wherein the controller is configured to control to perform rangingbetween the MS and the serving BS or between the MS and the neighboringBS, store a result by performing UL coarse beam selection, and determinethe UL Tx beam of the MS or the UL Rx beam of the serving BS or theneighboring BS.
 45. The apparatus of claim 42, wherein the NW-HO requestmessage comprises at least one of mobile station identifier indicatingan identifier of the MS to hand over, DL beam identifier indicating theDL Tx beam to be used by the corresponding neighboring BS to transmitdata to the MS after the handover of the MS is completed, and UL beamidentifier indicating the UL Rx beam to be used by the correspondingneighboring BS to receive data from the MS after the handover of the MSis completed, wherein the handover of the MS is a network re-entry,wherein the UL beam identifier is contained when the MS and thecorresponding BS perform the association.
 46. The apparatus of claim 42,wherein the NW-HO response message comprises at least one of mobilestation identifier indicating an identifier of the MS to hand over, DLbeam selection indicating whether the MS performs DL beam selection forthe corresponding neighboring BS, UL beam selection indicating whetherto perform UL beam selection when the MS hands over to the correspondingneighboring BS, dedicated ranging used when the UL beam selection is setand the corresponding neighboring BS allocates a dedicated ranging codeor a dedicated ranging opportunity for fast handover of the MS, actiontime indicating a time for using the dedicated ranging code when thededicated ranging is set, and indicating a time for transmitting andreceiving actual data when the DL beam selection is not set and the ULbeam selection is not set, dedicated ranging code contained when thededicated ranging is set, period for dedicated ranging code containedwhen the dedicated ranging is set and indicating a valid time of thededicated ranging code to be used by the MS, and dedicated random accesschannel pattern identifier indicating an index of a scheduling patternof dedicated random access channel ranging opportunity allocated by theBS to the corresponding MS when the dedicated ranging is set.
 47. Theapparatus of claim 42, wherein the NW-HO confirm message comprises atleast one of mobile station identifier indicating an identifier of theMS, base station identifier indicating the identifier of the BS whichthe MS determines to hand over to, and last sequence numbers (SNs)indicating a sequence number of a last packet successfully used perservice flow of the MS and provided as many as the service flows of theMS.